1. Field of the Invention
The present invention relates to a power controller that performs electric power generation by using DC power generation means, for example, a fuel cell, or the like.
2. Related Art of the Invention
Heretofore, a system shown in FIG. 7 is known as a fuel cell power generation system (for example, refer to Japanese Patent Laid-Open No. 6-325774). In FIG. 7, a fuel cell 41 makes hydrogen, supplied by hydrogen supply means 42, and oxygen in air, which is supplied by air supply means 43, react in a main body of the fuel cell to generate DC power, which is converted into AC power by a power converter 44 and is outputted. A controller 45 can perform control so as to variably output electric power by electrical discharge from a charge and discharge apparatus 46 or charge to the charge and discharge apparatus 46 even if the generated power of the main body 41 of the fuel cell is fixed, by controlling the charge and discharge apparatus 46 and power converter 44.
Nevertheless, though it is necessary in such a fuel cell power generation system to match an output voltage of the main body 41 of the fuel cell to charge and discharge voltages of the charge and discharge apparatus 46, the charge and discharge apparatus 46 does not have means of controlling charge and discharge. Hence, it is difficult to control the charge and discharge of the charge and discharge apparatus 46 in high accuracy by compensating the difference between the output of the main body 41 of the fuel cell and ratings of power storage means such as a secondary cell in the charge and discharge apparatus 46.
The following system is conceivable for canceling such a fault. FIG. 8 shows a configuration of a fuel cell power generation system according to a second conventional example. In FIG. 8, a fuel cell 51 is a main body of a fuel cell to generate DC power by reacting hydrogen with oxygen in air. A DC/DC converter 52 boosts a voltage of DC power of the fuel cell 51. A power converter 53 (inverter) converts the DC power, boosted by the DC/DC converter 52, into AC power to output the AC power to an electric power load 55. A controller 54 is the means of detecting a load current of the electric power load 55 by a load current detector 56 and controlling a two-way DC/DC converter 57, the DC/DC converter 52, and the power converter 53.
The controller 54 stores electric power in a storage battery 58 through the two-way DC/DC converter 57 when a value of an output current from the main body 51 of the fuel cell according to the load current of electric power load 55 exceeds a load current value. When a value of the output current from the main body 51 of the fuel cell is insufficient for the load current value, the controller 54 supplies the electric power of the storage battery 58 to the electric power load 55 through the two-way DC/DC converter 57.
The fuel cell power generation system according to the above-mentioned second conventional example (FIG. 8) has a configuration in which the power converter 53 is connected to the two-way DC/DC converter 57 for the charge and discharge control of the storage battery 58 coupled with an output of the DC/DC converter 52 that boosts DC power to a voltage necessary for converting DC power into AC power.
This system is made not only to control an output of the main body 51 of the fuel cell by the DC/DC converter 52, but also to raise charge and discharge efficiencies of the storage battery 58 by controlling the two-way DC/DC converter 57. Accordingly, charge from the fuel cell 51 to the storage battery 58 is performed through two voltage control means of the DC/DC converter 52 and two-way DC/DC converter 57.
Nevertheless, since there is large difference between charge and discharge voltages of the storage battery 58 and an output voltage boosted by the DC/DC converter 52 (in general, the output voltage boosted by the DC/DC converter 52 is higher), it is necessary to increase the difference between step-up voltages and step-down voltages of the two-way DC/DC converter 57 according to the above difference. Hence, it is difficult to raise power conversion efficiency.
Moreover, there are issues that operating economy is low since total power conversion efficiency which is a product of a power conversion efficiency of the two-way DC/DC converter 57 and charge and discharge efficiencies of the storage battery 58 becomes low, in addition, cost also becomes high since a price of the two-way DC/DC converter 57 itself is also high.
In consideration of the above-mentioned issues, the present invention provides a fuel cell power controller, which quickly corresponds to a change of electric power demand, highly effectively generates electric energy required, and is highly economical and reliable, a power generation system using it, or the like.
One aspect of the present invention is a power controller comprising:
power storage means of storing DC power outputted from DC power generation means that generates DC power;
power conversion means of including at least a DC/DC converter that converts a voltage when receiving a DC input;
charge and discharge means of discharging electric power from the power storage means to the power conversion means and of charging DC power from the DC power generation means in the power storage means, the charge and discharge means being provided among the DC power generation means, the power storage means and the power conversion means;
detection means of detecting electric energy of an external power load to which power from at least the power conversion means is supplied; and
control means of controlling operation of the charge and discharge means on the basis of the detected electric energy,
wherein the charge and discharge means has a DC/DC conversion function, converts an output voltage of the DC power generation means into a charge voltage of the power storage means, and converts a discharge voltage of the power storage means into an output voltage of the DC power generation means.
Another aspect of the present invention is the power controller, according to the 1st invention.
wherein the control means performs control of making the charge and discharge means perform the charge operation when the external power load is low, and making the charge and discharge means perform the discharge operation when the external power load is high.
Still another aspect of the present invention is the power controller, according to the 1st invention,
wherein the amount of converted voltage between an output of the DC power generation means and an input of the power storage means is smaller than the amount of converted voltage between an output of the DC power generation means and an input of the DC/DC converter of the power conversion means.
Yet still another aspect of the present invention is the power controller, according to the 1st invention, wherein the charge and discharge means comprises:
charge side conversion means of converting an output voltage of the DC power generation means into a charge voltage of the power storage means; and
discharge side conversion means of converting a discharge voltage of the power storage means into an output voltage of the DC power generation means.
Still yet another aspect of the present invention is the power controller, according to the 1st invention, wherein the charge and discharge means comprises:
common conversion means of performing a charge side conversion operation in which an output voltage of the DC power generation means is converted into the charge voltage of the power storage means or a discharge side conversion operation in which a discharge voltage of the power storage means is converted into an output voltage of the DC power generation means;
a first control switch of performing control so that an input side of the common conversion means is connected to an output side of the DC power generation means or an output side of the power storage means; and
a second control switch of performing control so that an output side of the common conversion means is connected to an input side of the DC/DC converter or an input side of the power storage means, and
when the charge side conversion operation is performed, the first control switch connects the output side of the DC power generation means to the input side of the common conversion means while the second control switch connects the output side of the common conversion means to the input side of the power storage means, and
when the discharge side conversion operation is performed, the first control switch connects the output side of the power storage means to the input side of the common conversion means while the second control switch connects the output side of the common conversion means to the input side of the DC/DC converter.
A further aspect of the present invention is the power controller, further comprising output voltage detection means of detecting an output voltage of the DC power generation means,
wherein on the basis of the detected output voltage and the detected load power, the control means makes the charge and discharge means perform the charge operation when the detected output voltage is high and the detected load power is low, and makes the charge and discharge means perform the discharge operation when the detected output voltage is low and the detected load power is high.
A still further aspect of the present invention is the power controller, further comprising power storage detection means of detecting power storage of the power storage means,
wherein the control means controls operation of the charge and discharge means on the basis of the detected power storage.
A yet further aspect of the present invention is the power controller, further comprising loadpower measurement means of measuring the detected electric energy as a function of time,
wherein a power generation schedule of the DC power generation means is determined on the basis of electric energy measured beforehand by the electric load power measurement means.
A still yet further aspect of the present invention is the power generation system comprising:
the power controller according to the 1st invention;
DC power generation means of generating DC power; and
control means of DC power generation means of controlling input energy of the DC power generation means on the basis of the detected electric energy.
An additional aspect of the present invention is a control method of the power controller,
wherein the electric energy is measured as a function of time, and
a power generation schedule of DC power generation means is determined on the basis of the electric energy obtained by the measurement.